In the past numerous fin designs have been effected for contributing to the roll or spin stabilization of missile means and the like as it follows its trajectory or flight path once launched from a platform such as, e.g., an aerial platform. For example, U.S. Pat. No. 2,271,280 to Weinert concerns a projectile provided with a plurality of collapsed stabilizing vanes until the projectile is launched from a gun bore. U.S. Pat. No. 3,643,599 to Hubich concerns missile means having combined retractible roll or spin-stabilizing fin means and drag-brake fin means; all for enabling control of the trajectory of the missile means before target impact. U.S. Pat. No. 3,978,790 to Sandelius concerns a sonobuoy having a series of spring biased retractible spin-stabilizing fins and also having a series of retractible drag-brake means for retractably mounting the spin-stabilizing means. When the sonobuoy is launched from a platform and after a predetermined time interval in its trajectory, the extended stabilizing fins are separated from the drag-brake means once the drag-brake means are extended (just before the sonobuoy impacts its target) from a collapsed position to an outward extended position. U.S. Pat. No. 5,211,358 to Bagley discloses missile means having a series of retractible roll or spin-stabilizing fin means that are pneumatically secured in an extended position once the missile means is launched. However, none of the aforediscussed references whether taken alone or in any combination remotely suggest the improved collapsible, roll or spin-stabilizing fin subassembly means of the instant invention for concentric attachment to missile means and the like at the trailing end thereof. The improved subassembly means is advantageously comprised of base or hub means, a plurality of fork means and a plurality of fin means; all components of the subassembly means being of relatively lighweight molded construction. By reason of the double axis relationship and double hinging (pivotal) action of the subassembly means as designed; it advantageously provides efficient, enhanced coin pact storage of the fin means between the missile means and the storage container means when the fin means are collapsed. Also, the fin means upon launch of the missile means are extended from their collapsed storage position rearwardly and outwardly to a uniform swept-back partially rotated position, such that the uniquely extended trailing and swept-back fin means effectively roll or spin stabilize the missile means against yaw and pitch as the launched missile means follows its intended trajectory with greater precision than heretofore possible.